The Optical Transport Network (OTN) is a technique of digital wrapper disclosed in 1999 to solve the problem of high capacity transmission for high speed Time Division Multiplexing (TDM) signals. The OTN defined in the version of 2003 can provide functions such as transmission, multiplexing, protection and monitoring management and so on for client layer signals, the supported client layer signals are mainly Ethernet signals supported by the Synchronous Transmission Module Level N (STM-N) and Asynchronous Transmission Module (ATM) and supported through the Generic Framing Procedure (GFP), and the defined rate levels are 2.5G, 10G and 40G. With the Internet Protocol (IP) normalization for the transport network bearing signals and the popularization of a 10G Local Area Network (LAN) interface, the bearing of 10 Gigabit Ethernet (10GE) on the OTN becomes an important problem. Therefore, the International Telecommunication Union Telecommunication Standardization Sector (ITU-T) developed a supplement standard (i.e. the G.sup43 standard) for the G.709 in 2007, which defined the mode of the OTN transmitting 10GE signals.
A multiplexing system of a traditional OTN is extremely simple. And the rate levels are 2.5G, 10G and 40G, which correspond to an Optical channel Data Unit (ODU)1, ODU2, ODU3 respectively. Services of Constant Bit Rate (CBR) are mapped to corresponding ODUks by the way of Asynchronous Mapping Procedure (AMP) or Bit-synchronous Mapping Procedure (BMP), Packet services are mapped to the ODUks by the way of GFP, and then these ODUks are mapped to corresponding Optical channel Transmission Unit (OTU)ks. Certainly, the ODUs with low rate level also can be multiplexed to the ODUs with high rate level as shown in FIG. 1.
In order to adapt to multiple services, a new concept of High Order (HO) ODU and Low Order(LO) ODU is introduced in the OTN, as shown in FIG. 2, counting from the left in FIG. 2, the first column is the LO ODU, the rate levels in all frames, such as the rate level of the ODU 3, are marked as ODU3(L), and L is precisely the Low Order; the second column is the HO ODU, the rate levels in all frames, such as the rate level of the ODU3, are marked as ODU3(H), and H is precisely the High Order. The HO/LO is identical with the concept of high order/low order container in a Synchronous Digital Hierarchy (SDH), the LO ODU is equivalent to that a service layer is used to adapt to services with different rates and formats, the HO ODU is equivalent to that a tunnel is used to provide transmission capability with certain bandwidths, this layering structure supports the separation between a service board card and a circuit board card, which thus can bring more flexibility and economy to the network deployment.
Compared with the G.709, the G.709 Amendment 3 and G.sup 43 have changed greatly, and new signal types are introduced, which includes ODU0, ODU2e, ODU3e1, ODU3e2, flexible ODU (ODUflex) and ODU4. The new optical channel data unit ODU0 with a rate of 1.244 Gb/s is firstly introduced, the ODU0 can be cross-connected independently, and also can be mapped to the high order ODU (such as the ODU1, ODU2, ODU3 and ODU4). In order to adapt to the transmission for 100GE services, the ODU4 is introduced, and the rate is 104.355 Gb/s.
The ODU1 is mapped to the ODU2 and ODU3 and the ODU2 is mapped to the ODU3 by keeping a 2.5G branch timing sequence mapping and multiplexing mode of the original version G.709, and 1.25G branch timing sequences is added with the ODU1 being mapped to the ODU2 and ODU3, and a 1.25G branch timing sequence is added with the ODU2 being mapped to the ODU3; all the other new rates (the ODU0, ODU2e and ODUflex) are mapped to the ODU1, ODU2, ODU3 and ODU4 with a 1.25G branch timing sequence mapping and multiplexing mode. According to the G.sup 43, the ODU2e can be mapped to a 2.5G branch timing sequence of the ODU3e1, and the ODU2e also can be mapped to the 1.25G branch timing sequence of the ODU3e1. Most of the low order ODUs have the same number of branch timing sequences in the high order. However, the ODU2e is an exception, and the ODU2e needs to occupy 9 1.25G branch timing sequences or 5 2.5G branch timing sequences in the ODU3, but needs to occupy 8 1.25G branch timing sequences in the ODU4. FIG. 3 is a detailed mapping and multiplexing path structure of the G.709 standard and G.sup43 standard.
The idea of Flexible ODU was widely discussed at the ITU-T Q11/SG15 intermediate meeting in September, 2008 and the ITU-T SG15 plenary meeting in December, 2008 initially. The initial thought of Flexible ODU is to provide bit transparent transmission of the OTN for client signals with arbitrary bit rates. The ODUflex is currently expected to be used for supporting those new bit rates which can be mapped to the ODU2, ODU3 or ODU4 effectively. The ODUflex is taken as one low order ODU; one ODUflex occupies the branch timing sequences whose number is the arbitrary integral multiple of branch timing sequences of the high order ODUk. The ODUflex bandwidth can be adjusted dynamically.
Currently, the size of Packet ODUflex is recommended to be: n×1.24416 Gbit/s±20 ppm (1≦n≦80), and the size of CBR ODUflex is 239/238 times of the client signal rate. The newly defined ODUflex will not provide mapping for the client signals which have been mapped to the ODU0, ODU1, ODU2 and ODU3 any more. With regard to CBR client signals, it is the first choice to map the client signals to the ODUflex through the BMP, and the ODUflex rate is 239/238 times of the client signal rate (above the 2.5G client signal rate). With regard to Packet service client signals, it is currently discussed that the client signals are mapped to the ODUflex using the GFP; ODUflex=n*1.24416G, wherein 1≦n≦80; and the ODUflex bit rate is integer multiple of the number of branch timing sequences of the high order ODUk.
After the G.709 standard of version 2003 is released, OTN devices are deployed abundantly after the development for several years, and the latest G.709 standard are also changed largely, after the newly deployed OTN devices are loaded with control planes, one end-to-end label switching path may control a great many old devices and new devices simultaneously, the old devices can only support a 2.5G branch timing sequence unit, and the new devices can support both the 2.5G branch timing sequence unit and 1.25G branch timing sequence unit; when one end-to-end label switching path goes through the old devices and new devices, the related interconnections during the management of end-to-end services become a technical problem existing in the reality.
As shown in FIG. 4, the OTN has been deployed in the network, the implementation of all node devices in the OTN is based on the G.709 standard version released in 2003, and each node in the network does not support the ODU0 and ODUflex and is based on the 2.5G branch timing sequence. With the larger-scale application of data services, operators need to introduce the applications of ODU0 and ODUflex into the existing network, when the applications of the ODU0 and ODUflex are introduced into the existing network, a problem of interconnection between the networks supporting the 1.25G Timing Sequence (TS) and the deployed networks supporting the 2.5G TS occurs, if no other technologies are introduced, the operators have to upgrade all nodes in the existing network to support the ODU0 and ODUflex, and this certainly will destroy the OTNs which have been invested by the operators.
One end-to-end ODUk service may go through a great many old devices and new devices simultaneously, the old devices can only support the 2.5G branch timing sequence unit, and the new devices can support both the 2.5G branch timing sequence unit and 1.25G branch timing sequence unit; when one end-to-end ODUk goes through the old devices and new devices, the related interconnections during the management of end-to-end services become a technical problem existing in the reality. Meanwhile, the problem of introducing services of the ODU0 and ODUflex into the OTN to perform interconnection with the deployed networks also occurs.